1. Field
The invention relates to medical imaging, particularly in percutaneous interventions.
2. State of the Art
During percutaneous treatment of vascular diseases, X-ray angiographic imaging is used to guide the intervention procedure. Detailed information of the diseased vessel, for example atherosclerotic plaque, is assessed by intravascular imaging modalities, such as intravascular ultrasound (IVUS) or optical coherence tomography (OCT), during the intervention procedure. Another example of an intravascular imaging modality is intravascular fractional flow reserve (FFR) in which the pressure within the vessel is measured during pullback.
The subject invention relates to all intravascular imaging devices having a controlled pullback speed. Intravascular imaging is performed during pullback of an intravascular device through a vessel and produces a stack of images showing vessel cross sections.
With this imaging modality it is difficult to correlate the position of a particular image with respect to its location in the vessel within an angiographic view. In practice the physician looks for anatomical landmarks, for example bifurcations or a number of side branches that can be recognized both on X-ray angiography and on the intravascular images in order to correlate the information of both imaging modalities with each other. However, this is time-consuming and prone to errors which might not lead to optimal treatment of vessel diseases.
US Patent Application Publication No. 2012/0059253 relates to a method of co-registration of intravascular images with X-ray images by tracing the intravascular transducer, which is located on the tip of the guide-wire, during pullback on X-ray fluoroscopy. This method has the disadvantage that the patient has an additional X-ray exposure, since X-ray fluoroscopy is necessary during the complete pullback of the intravascular device. During a percutaneous coronary intervention procedure, for example, the length of the coronary artery of interest can be up to 15 cm. With a motorized pullback speed of 0.5 mm/sec this would lead to an additional X-ray exposure time of 5 min. Although X-ray exposure can be reduced by means of ECG gated X-ray imaging, still the patient receives additional X-ray exposure. Another disadvantage of this method is the limited accuracy of length assessment due to foreshortening or out-of-plane magnification errors, which is important when choosing the correct stent- and/or balloon-length during treatment of the vascular disease.
U.S. Pat. No. 7,729,746 relates to a method in which the co-registration between X-ray and intravascular images is performed by generation of a 3D reconstruction of the vessel based on two X-ray angiographic projections. In order to perform the co-registration, two additional X-ray fluoroscopic images are required in which the user identifies in each fluoroscopic image the tip of the intravascular transducer. This results in a 3D point in space which is used to perform the co-registration. This approach goes in the right direction since the 3D reconstruction of the vessel of interest eliminates foreshortening and out-of-plane magnification errors, although the incorrect assumption is made that the centerline of the 3D model corresponds with the intravascular path in the vessel during pullback. Furthermore, any errors in the 2D segmentation of the vessel within the X-ray angiographic images will negatively influence the co-registration since they directly affect the 3D reconstruction of the vessel and its resulting centerline. Another disadvantage is that four additional X-ray images are required for this method resulting in additional exposure to the patient.
A further disadvantage of the prior art is that the true imaging plane within the space occupied by the intravascular electronics is not taken into consideration.